pierceessentials3e

The Importance of Polyploidy in Evolution

Polyploidy, particularly allopolyploidy, often gives rise to new species and has been particularly important in the evolution of flowering plants. Occasional genome doubling through polyploidy has been a major contributor to evolutionary success in several groups. For example, Saccharomyces cerevisiae (yeast) is a tetraploid, having undergone whole-genome duplication about 100 million years ago. The vertebrate genome has duplicated twice, once in the common ancestor of jawed vertebrates and again in the ancestor of fishes. Certain groups of vertebrates, such as some frogs and some fishes, have undergone additional duplications. Cereal plants have undergone several genome duplication events. The types of chromosome mutations we have discussed in this chapter are summarized in Table 6.3.

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TABLE 6.3 Different types of chromosome mutations

Chromosome mutation	Definition
Chromosome rearrangement Chromosome duplication Chromosome deletion Inversion Paracentric inversion Pericentric inversion Translocation Nonreciprocal translocation Reciprocal translocation	Change in chromosome structure Duplication of a chromosome segment Deletion of a chromosome segment Deletion of a chromosome segment Inversion that does not include the centromere in the inverted region Inversion that includes the centromere in the inverted region Movement of a chromosome segment to a nonhomologous chromosome or to another region of the same chromosome Movement of a chromosome segment to a nonhomologous chromosome or to another region of the same chromosome without reciprocal exchange Exchange between segments of nonhomologous chromosomes or between regions of the same chromosome
Aneuploidy Nullisomy Monosomy Trisomy Tetrasomy	Change in number of individual chromosomes Loss of both members of a homologous pair Loss of one member of a homologous pair Gain of one chromosome, resulting in three homologous chromosomes Gain of two homologous chromosomes, resulting in four homologous chromosomes
Polyploidy Autopolyploidy Allopolyploidy	Addition of entire chromosome sets Polyploidy in which extra chromosome sets are derived from the same species Polyploidy in which extra chromosome sets are derived from two or more species

Chromosome mutation

Definition

Chromosome rearrangement

Chromosome duplication

Chromosome deletion

Inversion

Paracentric inversion

Pericentric inversion

Translocation

Nonreciprocal translocation

Reciprocal translocation

Change in chromosome structure

Duplication of a chromosome segment

Deletion of a chromosome segment

Inversion that does not include the centromere in the inverted region

Inversion that includes the centromere in the inverted region

Movement of a chromosome segment to a nonhomologous chromosome or to another region of the same chromosome

Movement of a chromosome segment to a nonhomologous chromosome or to another region of the same chromosome without reciprocal exchange

Exchange between segments of nonhomologous chromosomes or between regions of the same chromosome

Aneuploidy

Nullisomy

Monosomy

Trisomy

Tetrasomy

Change in number of individual chromosomes

Loss of both members of a homologous pair

Loss of one member of a homologous pair

Gain of one chromosome, resulting in three homologous chromosomes

Gain of two homologous chromosomes, resulting in four homologous chromosomes

Polyploidy

Autopolyploidy

Allopolyploidy

Addition of entire chromosome sets

Polyploidy in which extra chromosome sets are derived from the same species

Polyploidy in which extra chromosome sets are derived from two or more species

CONCEPTS

Polyploidy is the presence of extra chromosome sets. Autopolyploids possess extra chromosome sets from the same species; allopolyploids possess extra chromosome sets from two or more species. Problems in chromosome pairing and segregation often lead to sterility in autopolyploids, but many allopolyploids are fertile.

CONCEPT CHECK 7

Species A has 2n = 16 chromosomes and species B has 2n = 14. How many chromosomes would be found in an allotriploid of these two species?

21 or 24
42 or 48
22 or 23
45